1. Field of the Invention
The present invention relates to a motor driving circuit, and more particularly, to a power saving driving circuit including power factor correction for an AC motor, capable of saving power by charging a power factor correction capacitor with a flyback voltage accumulated in a coil of the motor in normal operation mode and operating the motor with a discharge voltage of the capacitor in a power saving mode.
2. Description of the Related Art
Typically, an AC drive control technology has limitation in distribution due to a high design cost and circuit complexity despite of persistent development thereof. In particular, an inverter noise, such as harmonics or high frequencies, is usually a critical issue of an inductive circuit control using switching elements for a long time.
FIG. 1 illustrates a typical motor driving circuit. The typical motor driving circuit includes a converter 12 converting an AC power supply voltage into a DC power supply voltage, an inverter 14 receiving the DC power supply voltage from the converter 12 and driving the motor 20 according to a control signal from a controller 16, an encoder 22 detecting a rotation speed of the motor 20, and the controller 16. The motor 20 is an AC motor and various documents are published regarding to a control of the rotation speed for the motor.
However, such a typical motor driving circuit has limitations in that power consumption in an internal circuit is high and production costs are high due to complexity of voltage & frequency (VF) control using a pulse width modulation (PWM) signal. In particular, preparations of a converter for AC-to-DC-converting, an inverter for DC-to-AC-inverting, and an electromagnetic interference (EMI) filter circuit including a power factor correction (PFC) circuit for limiting harmonics/high frequencies cause an entire cost increase together with a cost according to complexity of the speed control using the PWM signal. In addition, due to use of a separate inductor, a typical PFC circuit causes a cost increase and is susceptible to component damage due to an instant current change (di/dt) or an impulse current generation in a switch ON state.
Furthermore, a phase control scheme, which is mainly used in speed control of a cheap AC motor, is a chopped AC scheme for modulating a motor applied voltage waveform by directly using a triode for AC (TRIAC) without the converter/inverter circuit, and is a scheme for controlling a rotation speed by increasing slip of a motor. According to the scheme, a circuit configuration is simple, design thereof is relatively easy, and power consumption of the internal control circuit is low. However, a speed control is not precise and it is difficult to correct a power factor because of instability of a current waveform according to motor characteristics appeared during the voltage phase control.    Patent literature 1: Korean patent No. KR20-0354200 Y1    Patent literature 2: Korean patent No. KR10-0583189 B1